We analyze the distribution of MIMO channel capacity for different antennas in 2-D and 3-D statistically isotropic environments. These represent possible test environments that may be generated by multi-probe anechoic and reverberation chambers, respectively. We observe that the two environments yield comparable capacity distributions provided that 1) the 2-D statistically isotropic environment's capacity data is taken at many different antenna orientations, and 2) the radiation elements have a low directivity. When these conditions are met, we find that the relative error between the 2-D statistically isotropic environment's orientation-combined capacity distribution and the 3-D statistically isotropic environment's capacity distribution is typically less than 10% for signal-to-noise ratio's greater than 5 dB.